Friends and family are worried that it is Sharita Williams, 35, a medical assistant who worked at the Park Medical Centers building and was reported missing after employees were told to evacuate shortly before 9 a.m. Police have not identified the remains.

The gunman, believed to be either a current or former maintenance worker for the building, also was reported missing but his body has not been found.

Williams had been dating a man she met at work, said Angelo White, 32, her ex-boyfriend and longtime friend. After about six months, she decided to break off the relationship but had trouble with the man, whom White identified as Myron Williams. The two were not related.

"She wanted to go on with her life," White said.

Sharita Williams' mother, Antha Williams-Hill, drove to the scene as construction crews dug through the rubble of the building.

"I've been trying to get in touch with her since this morning," Williams-Hill said. "I turned on the news and saw the building and said, 'Oh Lord!' "

Sharita Williams had moved to Southfield, Mich., a Detroit suburb to get away from Myron Williams, her mother said. Last week, her daughter, who has four children, was granted a personal protection order against the man.

An official familiar with the investigation said authorities believe Sharita Williams and Myron Williams were both inside the building as the fire raged.

Lanier Alfaro, an office manager at a podiatrist's office in the building said she was told that the man had targeted a woman who worked in the building and the two might have had a dispute.

"There was some type of altercation, some type of problems prior," said Inspector Dwane Blackmon, head of homicide at the Detroit Police Department. He would not offer additional details.

"Initially, what we know is that it was an arson fire," he said. "It was started by an individual who we believe fired shots prior to the fire being started."

Detroit firefighters largely had extinguished the flames by late morning. Smoke continued to rise from the building as police interviewed witnesses.

"It was devastating," Alfaro said.

Dr. Stuart Kirschenbaum stood with his family, watching bulldozers take down the place he had worked for 30 years.

He said when he arrived at 6:45 a.m., he saw the maintenance man believed to be the shooter, but that was normal. At about 8:30 a.m., security guards in the building came and ushered out people inside, saying that the maintenance man had taken two women hostage and had shot one before heading down to the basement.

Police reported only two missing persons, including the gunman.

The fire also has claimed the extensive boxing memorabilia collection of Kirschenbaum, a former Michigan Boxing Commission member.

"The killings, then burning the building down. It's just affected thousands of people," he said. The number of doctors in the building made it one of the largest health care providers in the area.